Determination of Water Consumption and Productivity of Wheat in Different Irrigation Systems in Behbahan

Precise estimation of the amount of water consumed, irrigation efficiency and water productivity of crops are the most important key indicators in agricultural sector planning of Iran. The figures given for the volume of water used in the agricultural sector are very different and there are serious doubts as to their accuracy. The average of water use efficiency in the country is 1.32 kg/m3 and its annual growth in the last 11 years has been reported to be 0.041 kg/m3 (Abbasi et al., 2017). Therefore, it is necessary to carry out an exploratory work that can be used to quantify the volume of water consumed by various products. Therefore, the main objective of this paper is to measure water consumption of wheat directly and to compare wheat water productivity in different irrigation systems under farmers management in Behbahan.

The volume of application water for wheat in different farms during one season (2016-2017) was measured and compared. The measured values were compared with the crop water requirement estimated by the Penman-Monteith and the national document. To determine the volume of water consumed, firstly, the flow rate of the selected water sources was measured, with the appropriate devices (flumes, meter and micro molina). Farm information including cultivated area, soil texture, soil electrical conductivity, electrical conductivity of the irrigation water used, and farm location with GPS were recorded. Other field information such as irrigation method, irrigation water sources (surface, underground), type of irrigation network (modern, traditional) were also recorded. Effective rainfall was calculated by the SCS method. Crop water requirement using the Penman-Monteith method was determined from data of current year and 10-year data for Behbahan city from the nearest meteorological station.

 32 wheat farms were selected and evaluated, of which 15 farms were irrigated with surface irrigation, 10 farms with sprinkler and 7 farms with drip irrigation systems. The results showed that the yield of wheat varied from 2000 to 6854 kg per hectare. The most water productivity of wheat occurred in a farm with drip irrigation being 2.79 kg/m3. Irrigation application efficiency varied from 22.7 to 99.7%. Updated crop water requirement changed from 373.4 to 517.0 mm. The highest water consumption was measured to be 4626 m3/ha in the farms receiving water from springs. The results of the t-Test analyses showed that the yield in drip irrigation farms (average being 5169 kg/ha) was significantly different as compared to sprinkler and surface irrigation systems with 3574 and 3795 kg/ha, respectively. The results of the comparison of the mean water productivity in the t-Test indicated that drip system with 1.51 kg/m3 of water productivity had the highest values and there was a significant difference with the two sprinkler and surface systems, which respectively had water productivity of 0.90 and 0.88 kg/m3. The Pearson correlation coefficients showed that the trend of changes in the amount of water consumed with the trend of changes in the application efficiency index and water productivity proved uncoordinated and it was significant at 1% level.

 The results of measurements in 32 farms showed that half of the drip irrigation fields were not cultivated on the recommended date range. Therefore, the growth period in this half was less than 140 days. Despite the decline in growing season and the non-observance of planting dates, yield in these farms was over 4000 kg ha-1. Application efficiency in sprinkler irrigation method was more than other irrigation methods. The reason for the high application efficiency in sprinkler irrigation was the backwardness of sowing date on one side and the late harvest of wheat on the other. The surface system with a growth period of 158 days had the highest growth period and has a significant difference with two dripping and sprinkler systems. The surface water system with the volume of water consumed at 4398.7 m3/ha had the highest volume of water consumed and showed a significant difference with the drip system, but this difference was not meaningful compared with the sprinkler system. The volume of water consumed by two systems of drip and sprinkler was measured at 3490.5 and 3863.6 m3/ha, respectively. The backwardness of wheat harvesting time in sprinkler irrigation fields caused the major filling time of the grains to be adjusted to April, which coincided with a higher increase in the air temperature. This led to increased water consumption at this particular time point and caused a significant decrease in water consumption despite the lower consumption of water in the sprinkler system.